1. Field of the Invention
The present invention relates to a dispersion that is autocrosslinking at room temperature, is composed of a mixture of at least two latex polymers of different glass transition temperature (Tg) and comprises a crosslinking agent that is active as the dispersion forms a film. The present invention is further directed to a process for the preparation of this dispersion and also to a method of using this dispersion as a binder for non-blocking, scratch-resistant and chemical-resistant coatings for, in particular, wood and plastics.
2. Description of Background Art
It is known from EP-A 0 466 409 that, by mixing a soft dispersion containing a latex polymer having a Tg of less than 20.degree. C. with a hard dispersion containing a latex polymer having a Tg in the range from 25.degree. to 65.degree. C., a binder is obtained that forms a film at room temperature without the addition of volatile organic solvents and which is used in highly blocking-resistant coatings. A disadvantage of these coatings, however, is their low resistance to chemical action, e.g., on contact with cleaning agents and beverages. A further disadvantage of these coatings is their low scratch resistance.
It is also known from EP-B 0 332 011 that, by mixing a hard dispersion prepared by stepwise emulsion copolymerization and having a minimum filming temperature (MFT) of from 65.degree. to 110.degree. C. with a softer dispersion having a MFT of from 20.degree. to 60.degree. C., viscoelastic, transparent and sandable films are obtained that are particularly suitable for the coating of wood. However, because of the relatively high MFT of the softer dispersion in this case, a relatively large quantity of a filming auxiliary must be used in order to ensure that the corresponding mixture forms a film at room temperature.
Moreover, EP-B 0 184 091 discloses that it is possible, by multistage emulsion polymerization, to prepare aqueous, autocrosslinking polymer dispersions that have a low MFT and form films of high blocking resistance. However, these films have deficiencies in terms of low scratch resistance.